Just curious, I can see in the example situations, line stretch, distance, climbers weight and sag specified.. It seems over-specified. Wouldn't the distance, sag and weight be sufficient for a static case ?

I assume that the line stretch must be a 'pre-tension' figure, but not sure how this would be applied in a calculation to improve the accuracy.

I get around 5.9kN for the 15M/0.5M/80Kg scenario. I am assuming half of the tape provides half of the vertical opposing force, with both adding together to 80*9.81 (if that makes any sense).

Shorty, 1kN is 100kg, 2kN is 200kg. Clearly a slackline is going to experience more force than that.

I really don't get the obsession with trying to theoretically calculate these things. How much does a 50kN steel screwgate cost these days? Just put one of those on, do up the screw, and there is no way in hell you'll ever get a biner breaking again........unless you're alpine slacklining, then every gram counts.

>Well, it may offer you some insight, so long as you know that it will>probably be wrong.>>"In theory there's no difference between theory and experience"

I appreciate both points. I'm more curious that obsessed.

Having some appreciation for the sorts of forces that might be involved in a slackline (relatively high) is precisely why I have steel carabiners. While it is true that the answers will always be wrong, it is good to know the ball parks you are operating in.

It is also to know what you don't know. Eg, the force we have been calculating is actually more of a minimum, and with dynamics it could be much larger.

On 9/09/2013 mikllaw wrote:>On 9/09/2013 One Day Hero wrote:>>I really don't get the obsession with trying to theoretically calculate>>these things. >>Well, it may offer you some insight, so long as you know that it will>probably be wrong.>>"In theory there's no difference between theory and experience"

"What is right in theory must work in practice.
And if it does not there is a mistake in the theory: Something has been overlooked and not allowed for and consequently what is wrong in practice is wrong in theory too."

On 9/09/2013 patto wrote:>Yes it is over specified. And yes, shortman doesn't know what he is talking>about.

I can see why Damo loves hangin shit on ya patto.

Are you semi-agreeing with a dude whose guestimate is closer to my guestimate than yours?

Over specified my big fat one....surely you could conjure some awesome maths to backup how more or less stretchiness absorbs energy. Or is that just an over specified detail because that online slackline calculator and ya fancy formulas can't allow for it?

On 9/09/2013 One Day Hero wrote:>Shorty, 1kN is 100kg, 2kN is 200kg. Clearly a slackline is going to experience>more force than that.

Big statement for a smart dude Damo. A slackline?? That's like saying - a fall. As in all falls are the same. Next time we catch up, I'll demonstrate....a short stretchy slackline.>>I really don't get the obsession with trying to theoretically calculate>these things. How much does a 50kN steel screwgate cost these days? Just>put one of those on, do up the screw, and there is no way in hell you'll>ever get a biner breaking again........unless you're alpine slacklining,>then every gram counts.

from my understanding though the real-life forces never get close to the theoretical forces though. I dont think the forces are as collossal as people make out. sure i've broken lines but that was being silly.

Most biners are stronger than the line used so i would get too worried. think those BD ovals are only 18kN? so while they're shitty for climbing, they have just proven to be shitty for everything!

From a close exam of the photo and remembering my materials lectures ( a while ago) there appears rotational failure evidence. Partial cupping and little bending and failure face. Would match location of failure to maximum moment as end rotated.

I'll say it again - CYCLIC LOADING! (As well as being under spec'd) . . .
It was a 'long term' setup and had no doubt seen tens of thousands of reasonably high load/release cycles from people bouncing on the line, leading to weakening at that point . .
The failure mode is similar to what I have seen in tests on biners run through cyclic load tests after similar failures in flight equipment - hanggliders etc
Climbing carabiners are not designed for long term cyclic loading, they are really designed for single large forces being occasionally applied . . .